1. Field of the Invention
The present invention relates to a uni-morph, bi-morph or other types of piezoelectric or electrostrictive actuators which undergo displacement in the form of bending, deflection or flexure and which can be used as or for displacement-controllable elements, solid element motors, relays, switching elements, camera shutters, print heads, pumps, fans or blowers, microphones, sounding bodies (such as a speaker), ink jet ejectors, and other components or devices. The term "actuator" used herein is a member capable of transducing or converting an electric energy into a mechanical force, displacement or strain.
2. Discussion of the Prior Art
Recently, an element whose displacement can be controlled has been widely used and increasingly needed in the fields of optics and precision positioning or machining operations, for example, for adjusting or changing an optical path length or the position of a member or component of a device, on the order of fractions of a micron (.mu.m). To meet this need, there have been proposed and developed various piezoelectric or electrostrictive actuators utilizing a piezoelectric or electrostrictive material such as a ferroelectric material, which exhibits the reverse or converse piezoelectric effect or the electrostrictive effect, in which such a piezoelectric or electrostrictive material produces a mechanical displacement upon application of a voltage or electric field thereto.
Conventionally, the piezoelectric/electrostrictive actuator is structurally classified into a mono-morph type, a uni-morph type, a bi-morph type and a lamination type. The mono-morph, uni-morph and bi-morph types provide a relatively large amount of bending or flexural displacement or deflection or distortion owing to the transverse mode of the reverse piezoelectric effect or electrostrictive effect, namely, due to the strain perpendicular to the direction of the electric field produced upon application of a voltage. These types, however, suffer from inherent problems such as a small magnitude of a force generated, a low response speed, and a low level of electro-mechanical conversion efficiency. On the other hand, the lamination type utilizes the longitudinal mode of the reverse piezoelectric effect or electrostrictive effect, namely, the strain parallel to the direction of the electric field, and therefore assures a large magnitude of the generated force, a high response speed, and a high level of electro-mechanical conversion efficiency. However, the lamination type suffers from an inherent problem that the amount of displacement produced is relatively small.
The conventional piezoelectric/electrostrictive actuator of the uni-morph or bi-morph type also suffers from a relatively low operating reliability, which arises from the use of a bonding agent for bonding together the component sheets or plates of the actuator such as piezoelectric/electrostrictive elements or layers.
Thus, the conventional piezoelectric or electrostrictive actuators have drawbacks as well as advantages, and suffer from some problems that should be solved.